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As an alternative to antibody,aptamer has a great potential as analytical tools for Paralytic shellfish toxin (PST) detection.In this article,high-affinity single stranded DNA (ssDNA) aptamer targeting F(ab')2 fragments of saxitoxin (STX) antibody was selected from a random ssDNA library by SELEX strategy.After 16 rounds of repeated selection,the highly enriched ssDNA library was sequenced and then all sequences were carefully identified by indirect enzyme linked assay and indirect competitive enzyme linked assay (icELISA).The candidate aptamers in the above identification were selected for further characterization by icELISA and the equilibrium filtration method.Finally,we successfully obtained an aptamer bearing the internal image of STX,whose apparent dissociation constant (Kd) was estimated to be 96.37 nM.Further work is in progress aimed at using this aptamer substitute STX standard for development of an aptamer/antibody-based nontoxic detection method for field determination of STX in seafood products.